Mstislav III Glebovich (before 1215/1220 – after October 18, 1239) was an Olgovichi prince. He was probably prince of Rylsk[1] (1212–1239/1241) and of Chernigov (1235–1239/1241).[1] During his reign, the Tatars (the Mongols) invaded and pillaged the towns of the Principality of Chernigov.[1]
He was the son of Prince Gleb Svyatoslavich of Chernigov and Anastasia Ryurikovna, a daughter of Grand Prince Ryurik Rostislavich of Kiev. His father died between 1215 and 1220.[1]
By 1225, Mstislav had already been second in seniority among the Olgovichi (the ruling dynasty of Chernigov), and therefore during the absence of his cousin, Mikhail Vsevolodovich, he commanded them.[1] On April 6, 1231, he attended a snem (a meeting of some leading princes of Rus’ organized by Grand Prince Vladimir III of Kiev) in Kiev, but the reasons for convoking the council are not given.[1] It appears that his domain probably lay west of the Snov and Desna rivers.[1]
Although the chronicles never tell us that he ruled Chernihiv, but his seniority merited him that post.[1] Moreover, the evidence that the onus of defending the town fell on his shoulders supports this.[1]
In the autumn of 1239, the Tatar horde advanced against Chernihiv along the northern shore of the river Seym.[1] Presumably, the invaders captured Hlukhiv, Kursk, Rylsk, and Putivl, and on reaching the river Desna, they advanced towards Chernihiv.[1] When Mstislav heard that the Tatars were attacking the town, he came with his troops to confront them.[1] The nomads used catapults that hurled stones the distance of a bowshot and a half.[1] Mstislav barely escaped, but many of his men were killed.[1] After Chernigov fell on October 18, the Tatars pillaged the towns in the surrounding countryside.[1]
Before departing from Chernihiv, the Tatars sent messengers to Kiev proposing peace, and they were pacified, we are told, with Mstislav.[1] The chronicler probably made only a passing reference to his capitulation in an effort to underplay the nature of his commitments.[1] He must have submitted to Batu Khan’s authority and agreed to campaign with him and to pay a tithe in everything.[1]
In 1241, his cousin, Mikhail Vsevolodovich, who had returned from Masovia when the Tatars invaded his lands, gave Chernihiv to his own son, Rostislav Mikhailovich.[1] Mikhail Vsevolodovich may have repudiated Mstislav because, contrary to his wishes, he had formed a pact with the enemy; or (although the chronicles fail to tell us) Mstislav may have died following his pact with the Tatars.[1] The possibility of his demise is implied by the silence of the chronicles, which never mention him again.[1]
The name of his wife is not known.